THE ANSWER
Starting with 1000, add 40, then 1000, followed by 30, another 1000, then 20, another 1000, and finally add 10.
The total is:
1000 + 40 + 1000 + 30 + 1000 + 20 + 1000 + 10 = 4090.
Also read: Think you’re smart? 95% of “smart people” can’t figure this out!